The invention relates to a process and device for supplying processing gas to a reactor located in a zone subjected to intense electric and/or electromagnetic fields likely to cause ionization of said gas.
It applies more particularly, but not exclusively, to supplying a processing device with processing gas by ionic bombardment, for example an ionic implanter of the type used in the semiconductor industry for incorporating ionized chemical species on silicon substrates for doping thereof.
In this example, the generation, acceleration and focussing of the ions bring into play considerable electric fields, requiring voltage sources of several tens of kilovolts.
This is why, for safety reasons, the reactor (or ionization chamber) in which the processing takes place is isolated, as well as the elements brought to said voltages situated in its environment, in a conducting enclosure serving as electric and/or electromagnetic screen which forms a potential barrier between its inner volume and its outer environment.
Because of the intensity of the intense electric fields present inside the enclosure, it is impossible during processing to admit the processing gases into the ionization chamber from gas sources situated outside the enclosure, particularly because of:
the impossibility of passing the metal pipelines through the enclosure (even in the case where these pipelines are sufficiently isolated with respect to the enclosure, these pipelines would be brought to high potentials and would form electric conducting bridges between the inner volume of the enclosure and its outer environment, PA0 the impossibility of causing the gases to flow through non conducting pipelines, because such gases would be ionized and would become conducting. PA0 the need to frequently replace the cylinders, such replacement involving opening the conducting enclosure after interrupting the high voltage supply and after making sure that no residual electric charges remain inside the enclosure, these operations only being able to be carried out during a prolonged shut-down of the reactor; PA0 handling difficulties due in particular to the compactness of the expansion panel associated with the gas sources and its position inside the enclosure, and PA0 a risk of contamination and corrosion of the equipment situated inside the enclosure during handling, such equipment being furthermore very expensive.
Considering these problems, the present solution consists in using processing gas reserves of small capacity (0.6 l in general) placed in a ventilated metal box, itself disposed inside the conducting enclosure and brought to the same potential as that of a high voltage source which supplies the reactor.
This solution has however several major drawbacks: